This invention relates to a rotary regenerative heat exchanging ceramic body for high temperature gases for use in gas turbine engines, Stirling engines and the like.
A rotary regenerative heat exchanging ceramic body of this type is in the form of a, honeycomb structure disk on the order of 20-200 in cm diameter and 2-20 cm in thickness having. Such a heat exchanging body is generally rotatably arranged to shut off two passages having semicircular cross-sections as obtained by dividing a circle into two parts.
A high temperature gas is caused to flow through one of the two passages during which the heat of the gas is absorbed in the heat exchanging ceramic body. The heat-exchanging body is then rotated so that it would give off heat to low temperature air which is counter-flowing in the other passage. In this case, temperatures of the gas are for example 1000.degree. C. at an entrance of the ceramic body and 200.degree. C. at an exit thereof, while temperatures of the air are 100.degree. C. at an entrance and 900.degree. C. at an exit. As the exhaust gas and the air are counter-flowing with each other, the entrance and the exit for the exhaust gas are closely adjacent the exit and entrance for the air, respectively, so that there are always temperature differences not less than 800.degree. C. in the heat exchanging body to cause severe thermal stresses therein.
Moreover, as outer circumferences of the heat exchanging body are exposed to atmosphere a low temperature atmosphere, there are temperature differences between a center portion and the outer circumferences of the body to cause separate thermal stresses in addition to the above thermal stresses. Therefore, the rotary regenerative heat exchanging ceramic body needs to possess high heat-exchanging efficiency, and at the same time resist the considerable thermal stresses in use.
A small type heat exchanging ceramic body may be produced by extruding a ceramic material into a unitary body. With ceramic bodies of middle or large type, however, matrix segments made of a ceramic material should be jointed to each other by a bonding material such as cement, ceramic, glass or the like.
Such rotary regenerative heat exchanging ceramic bodies made of jointed segments have been typically disclosed in Japanese Patent Application Laid-open No. 55-46,338 belonging to the applicant or assignee of the present case. As disclosed in the Laid-open Application, it had been found that a ceramic body having a number of joined matrix segments with directions of their cells being in parallel is likely to cause cracks in the proximity of the outer circumferences due to considerable tensile stresses in circumferential directions during use. The considerable tensile stresses result from the thermal stresses above described. As well known, the ceramic body is poor in tensile strength in comparison with compressive strength so that the cracks are caused by the tensile stresses.
In order to avoid such a disadvantage of the ceramic body, it has been proposed to combine matrix segments having a plurality of different cell shapes. In U.S. Pat. No. 4,381,815. However, the ceramic body disclosed in the United States Patent is complicated in manufacturing processes and very expensive because of the matrix segments required to have a plurality of different cell shapes.